1. Field of the Invention
This invention relates to a chip-type composite electronic component and a manufacturing method thereof, and more particularly, to a composite electronic component of a chip inductor and a chip thermistor, and the manufacturing method thereof.
2. Description of the Related Art
A conventional high frequency filter is described in Japanese Utility Model Pub. No. 6-50312 and includes a laminate-type chip inductor. In the chip inductor, laminated ceramic layers form a chip element, a wound coil wraps around the inside of the chip element to connect the coil conductor of a ceramic interlayer via a through-hole provided in a ceramic layer. Ends of the coil are connected to different external electrodes.
In this kind of laminated type inductor, the impedance depends on the composition and the specific resistance of a ceramic material, the aperture-diameter dimension and the number of turns of a coil conductor, and the width and the material of the coil conductor. However, once a product is made, the frequency characteristic of the impedance is fixed and cannot be changed.
To overcome the above-described problems, preferred embodiments of the present invention provide a small-sized chip-type composite electronic component in which the impedance can be changed depending on the temperature, and a manufacturing method thereof. Moreover, preferred embodiments of the present invention provide a chip-type composite electronic component with a stable impedance characteristic and a manufacturing method thereof.
A chip type composite electronic component according to a preferred embodiment includes an inductor formed by laminating a plurality of ceramic layers having an internal coil conductor, and a thermistor formed by laminating a plurality of ceramic layers having an internal electrode and a predetermined resistance-temperature characteristic. At least one end of the internal coil conductor of the inductor and at least one end of the internal electrode of the thermistor are connected to a pair of external electrodes.
Since the chip-type composite electronic component of preferred embodiments of the present invention include a chip inductor and a chip thermistor laminated together to define one chip, a small-sized composite electronic component is obtained. Moreover, since the resistance value changes depending on the temperature, a thermistor is used to vary the impedance automatically depending on the working temperature. Thus, an inductor with a desired temperature characteristic is obtained.
The inductor and the thermistor may be connected in series or in parallel.
For example, since the resistance value of the thermistor increases drastically at a predetermined temperature or higher, when connecting a positive-characteristic thermistor (PTC thermistor) in series with an inductor, the circuit can be interrupted at the predetermined temperature or higher. In other words, the switch characteristic at a predetermined temperature can be used. Moreover, when PTC thermistor is connected in parallel with an inductor, the characteristic of the inductor can be returned to the characteristic as it is at the predetermined temperature or higher.
With some inductors, when a working temperature goes up, the component shows a positive temperature characteristic. Therefore, in some inductors the impedance rises. In such a case, using a parallel-connected NTC thermistor with an inductor functions to compensate for the temperature rise, and the temperature characteristic of the L component and the temperature characteristic of a resistance component offset each other. Thus, the inductor with a stable temperature characteristic is obtained.
The composite electronic component of various preferred embodiments of the present invention is used as a chip high-frequency filter with the above temperature characteristics in AC power supplies. However, in a DC power supply, since it can be used as a chip thermistor, one component can be used for both applications.
In another preferred embodiment of the present invention, an inductor and a thermistor are connected via an intermediate insulating layer. As a method of joining an inductor and a thermistor, a method of integrally baking after laminating green sheets is preferably used, more particularly, a method of attaching the inductor and the thermistor, respectively, after a baking process of the inductor and the thermistor is also used.
By the method described above, a diffusion is generated in the interlayer of an inductor layer and a thermistor layer. As a result, since characteristic degradation of a ceramic occurs, an inductor layer and a thermistor layer are laminated at both sides of a diffusion-prevention layer. Thus, a diffusion is prevented by baking and characteristic degradation is prevented. Moreover, since there is no possibility to generate a diffusion, the intermediate insulating layer may be an adhesive layer. Borosilicate lead system glass, or other suitable material can be used as an adhesive layer.
In addition, if the middle-material of the thermal expansion coefficient of the inductor and the thermistor is used as the intermediate insulating layer, the peeling of the inductor and the thermistor accompanied by the temperature change is eliminated.
Other features, characteristics, elements and advantages of the present invention will become apparent from the following description of preferred embodiments thereof with reference to the attached drawings.